Algae,
which are important protists, are major photo synthesizers
in
fresh and salt
water. What are their
lives
all about? Like all
living things,
they have two important
tasks: to capture
energy and to leave offspring.
The algae that you
design must be able
to do both if they are
to survive.

Photo synthesizers
capture solar energy.
The chloroplasts in
their cells use light
energy to synthesize
glucose (a kind of sugar)
from water and carbon
dioxide. Therefore
your algae need access to light.

Important:
seaweeds
need access to light.

All
living things need water, and some
of the chemicals that
dissolve in water.
Algae that live under water
do not have to worry
about drying out, so
their survival strategies
are about light capture
and reproduction.

The
ocean offers a number
of different environments,
and algae
have evolved to survive
in each one. These environments
include the deep waters
of the open ocean, and
the shallow waters close
to the land.

to the ocean floor.
Organisms
dependent on
photosynthesis cannot
hope to live on the
bottom, which may be
miles below. To survive
in
the open ocean, seaweeds must float
on the surface of the
water, where the sun
shines brightly, and
the only the shade that
falls on the water is
that cast by clouds.

The photo synthesizers
here are mostly
different kinds of
single celled
organisms that we
call
phytoplankton.
We cannot see the
tiny individual
cells, but they are
abundant, and sometimes
these tiny cells even
change the color of
the water.
They are the base of
the food chain in
the ocean, and are
eaten by tiny
animals and the
young of larger
animals that we
refer to as
zooplankton.
Then larger animals eat
the zooplankton.
The members of the
phytoplankton, many
of whom are algae,
produce a good part
of our atmospheric
oxygen.

In addition to sunlight, the
phytoplankton also need minerals and nutrients. These are carried down to the coasts by rivers and runoff water, so the organisms near the land can use these resources. On the surface of the deep ocean the number of living creatures varies with the availability of nutrients. At certain times of year there is an upwelling of waters from deeper levels. These waters bring up chemicals from the deep levels, where dead animals and
seaweeds have drifted down and decomposed. When the nutrients are carried up, the surface of the ocean becomes thick with
phytoplankton, and
tiny photosynthesizes
and animals
form a vast floating
community. When nutrients are scarce, only a few organisms live in these sunny waters.
These organisms
reproduce very
quickly when
nutrients are
abundant,.

In addition to the
tiny algae, some
multicellular algae,
which we would call
seaweeds, may form floating
mats. These
maps form
in areas where sea
currents circle, like those
in the Sargasso Sea.
The Sargasso Sea has
large tangled masses
of a variety of kelp
and a whole ecosystem
of smaller algae
and
small and microscopic
animals. Larger floating
seaweeds may have special
structures that they
fill with gas, like
tiny, very tough balloons,
which help the
seaweed to float. These
palgae
get lots of light, but
they are at the mercy
of storms and winds.
They may get blown into
shallow water, or even
onto shore, where they
dry out and die.

Many
of these large
multicellular algae reproduce
vegetatively,
that is, they just grow,
and when pieces get
broken off by wind or
big waves the pieces
are also complete
seaweeds.
These floating surface
algae are most abundant in
warmer waters, because
chemical reactions (what
life does) take place
more quickly in warmer
temperatures. Those
in cold waters
grow more slowly than
algae in warmer seas.

Shallow
water may lie above
rocky, sandy, or muddy
bottoms. Water is usually
shallow close to land,
so floating algae in
shallow water risk being
thrown up onto the beach
by the tides and by
storms. Light can penetrate
for quite some distance
into clean water: our
textbook, The Earth
Atlas, says that
the "good light"
zone goes down 75 feet.
Many shallow water
algae are close to the surface
of the water, perhaps
only inches from the
surface. They find some
way to attach themselves
to the bottom of the
ocean so that they can
grow up toward the light
and not be swept away.

The
strategies that these
algae use depend on
what the bottom is like.
If the bottom is rocky,
seaweeds develop some
way of holding onto
it. On earth,
seaweeds develop structures called
hold holdfasts. These
are not roots, because
they do not absorb water
or nutrients: they just
hold onto a rock.
Kelp anchor themselves
with holdfasts.
Kelp may be up to
90 feet in length, and
they form undersea forests
alive with fishes and
other life forms.

Small
seaweeds also cling to
the rocks. Some of them
are only a few inches
long and cling to rocks
near the shore. Some
even appear in the challenging
intertidal zone, where
the rocks they cling
to may be out of water
for short periods of
time.

Where
the sea bottom is made
of sand or mud, there
is nothing for
algae to hold onto. Some
sea grasses in these areas develop
runners that grow through
the mud and help to
hold them down,
however,
seagrasses are not
algae: they are
land plants that
moved back into
the underwater
environment about
100 million years
ago on
earth. Sea grasses
are
real plants and so
have roots, which
allow them to live
in an area where
the algae that are
native to the sea
cannot survive..

Sometimes
there are places where
rivers flow into the
sea, carrying a lot
of silt (fine particles
of clay) with them.
These areas can be difficult
for photo synthesizers
to live in:
if they get buried by
the silt, they will
die from lack of light.

Algae
can grow more quickly
in warm water than in
cold water, because
chemical reactions occur
more quickly where there
is more heat. You would
expect to find many
water
seaweeds near the
equator where the water
is warm. However,
nutrients must also be present if the
seaweeds are to grow.

Where the water
is very cold, as in
arctic seas, you also
find phytoplankton,
and even algae that
live under the ice.
Seaweeds grow there because
deep sea currents bring
nutrients up from the
depths. Seaweeds are dependent on both
light and the availability
of the chemicals needed
for growth.

The
earliest organisms
were
able to develop only
because they
were under water. The
ultraviolet light contained
in unshielded solar
radiation kills living
organisms. Nothing could
live on the surface
of the earth until the
planet had enough oxygen
in the atmosphere to
allow the protective
ozone layer to form.
Water provided shielding
from this lethal radiation,
providing an environment
for the earliest forms
of life.
Later some of the
oxygen that the
cyanobacteria and
the algae produced
became the ozone
layer that protects
all earth dwellers.